[Qt-interest] How to clear QVector without releasing memory?

[Schimkowitsch Robert]

resize(0) does really seem to be an option here. The way I understood
the source code, it really will not free up memory when I resize the
vector. What bothers me a little is that I would rely on undocumented
behaviour here, i.e. it might change without notice.

But the way I see it, there IS no documented way to remove items without
deallocating memory. 

Robert Schimkowitsch


-----Original Message-----
From: qt-interest-bounces+robert.schimkowitsch=andritz.com at qt.nokia.com
[mailto:qt-interest-bounces+robert.schimkowitsch=andritz.com at qt.nokia.co
m] On Behalf Of Nikos Chantziaras
Sent: Friday, June 17, 2011 6:39 PM
To: qt-interest at qt.nokia.com
Subject: Re: [Qt-interest] How to clear QVector without releasing
memory?

On 06/17/2011 05:19 PM, Schimkowitsch Robert wrote:
> Hi,
>
> I have a QVector that I want to re-use many times as a buffer. As the
> application is long-running on a low memory device, memory
fragmentation
> might be an issue.
>
> To keep this in check, I would like to reserve() the QVector once,
with
> the maximum size I am going to need, and then re-use it without ever
> freeing up memory.
>
> The only ways to clear all items from the vector I found will also
> deallocate memory.
>
> What is the performace-optimal way to clear a QVector without
> deallocating memory?

QVector::resize(0).  It doesn't clear anything, which means it's as fast

as it can possibly get.  The docs are hinting that this does not 
deallocate memory:

"If you know in advance how large the vector will be, you can call this 
function, and if you call resize() often you are likely to get better 
performance."

Dot not use QVector::clear().  This one will deallocate memory, 
according the docs.
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